Viral load and heterosexual transmission of human immunodeficiency virus type 1
Abstract
Background and Methods We examined the influence of viral load in relation to other risk factors for
the heterosexual transmission of human immunodeficiency virus type 1 (HIV-1). In a community-based
study of 15,127 persons in a rural district of Uganda,
we identified 415 couples in which one partner was
HIV-1–positive and one was initially HIV-1–negative
and followed them prospectively for up to 30 months.
The incidence of HIV-1 infection per 100 person-years
among the initially seronegative partners was examined in relation to behavioral and biologic variables.
Results The male partner was HIV-1–positive in
228 couples, and the female partner was HIV-1–positive in 187 couples. Ninety of the 415 initially HIV-1–
negative partners seroconverted (incidence, 11.8 per
100 person-years). The rate of male-to-female transmission was not significantly different from the rate
of female-to-male transmission (12.0 per 100 personyears vs. 11.6 per 100 person-years). The incidence of
seroconversion was highest among the partners who
were 15 to 19 years of age (15.3 per 100 person-years).
The incidence was 16.7 per 100 person-years among
137 uncircumcised male partners, whereas there were
no seroconversions among the 50 circumcised male
partners (P<0.001). The mean serum HIV-1 RNA level
was significantly higher among HIV-1–positive subjects whose partners seroconverted than among those
whose partners did not seroconvert (90,254 copies
per milliliter vs. 38,029 copies per milliliter, P=0.01).
There were no instances of transmission among the
51 subjects with serum HIV-1 RNA levels of less than
1500 copies per milliliter; there was a significant dose–
response relation of increased transmission with increasing viral load. In multivariate analyses of logtransformed HIV-1 RNA levels, each log increment in
the viral load was associated with a rate ratio of 2.45
for seroconversion (95 percent confidence interval,
1.85 to 3.26).
Conclusions The viral load is the chief predictor of
the risk of heterosexual transmission of HIV-1, and
transmission is rare among persons with levels of less
than 1500 copies of HIV-1 RNA per milliliter. (N Engl
J Med 2000;342:921-9.)
©2000, Massachusetts Medical Society.
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